I spent a long time trying to troubleshoot my mailing lists until I discovered this unusual gmail behaviour.
Gmail does not display messages that have been sent from a mailing list – if you posted them to that list. This happens even though the mailing list software may modify them extensively (by adding to the Subject line, or adding a footer, for example)
It will also not display messages that were forwarded from another account that were initially sent by you.
There is no indication anywhere that these messages exist. They are invisible in Mail and Trash and Spam
If you want to test out a mailing list, you will need to post from another non-gmail account.
This may save you some time.